The Schengen Agreement concerns the removal of internal border checks between countries which have agreed to comply with the Schengen acquis (or body of law). It also provides for cooperation in police and judicial matters and sets rules for checks at external borders.
It has its roots in an agreement signed in 1985 between Belgium, France, the then Federal Republic of Germany, Luxembourg and the Netherlands. It was first incorporated into the European Union’s legal framework by a protocol to the 1997 Treaty of Amsterdam. Today, the Schengen Area consists of 22 EU member states and four non-EU member states.
The United Kingdom is not part of the Schengen Area but it does participate in the Schengen Information System which shares data between member states, and in certain police and judicial cooperation agreements.